PROCESS-CONTROL OF POLYMERIZATION REACTORS - AN INDUSTRIAL PERSPECTIVE

Polymerization reactors usually exhibit complex nonlinear dynamic beha vior because of the complexity of the physicochemical interactions and the kinetics of the polymerization reactions. In these reactors many important variables, often related to end-use polymer properties, cann ot be measured on-line or can only be measured at very low sampling fr equencies. Furthermore, end-use polymer properties are usually related to the molecular weight and composition distributions in the polymeri zation reactor. Finally, the typical industrial polymer reactor is use d to manufacture a variety of grades of the same basic product necessi tating frequent startups, on-line transitions, and shutdowns. The appr oaches used by the authors to meet these challenges are illustrated, w ithin the constraints of protecting proprietary information, by focusi ng on the modeling and control of a commercial multiproduct continuous emulsion copolymerization reactor. The development of fundamental pro cess understanding captured in a first-principles reactor model was a necessary prerequisite for the design of an efficient and robust syste m to control polymer properties. The model was verified with laborator y data and was used to represent quantitatively the effect of operatin g variables on the performance of the industrial reactor. The control system consisted of two levels namely the pressure, temperature, level , and flow regulatory control implemented in the Distributed Control S ystem and the advanced control of polymer properties implemented in th e supervisory computer. The structure of the feedforward and feedback control modules, which compute set points for the monomer and catalyst flows to effect on-aim control of reactor composition and inherent vi scosity are discussed. The benefits from the application of the advanc ed control system resulted in a significant improvement of the first-p ass, first-quality yield and polymer property uniformity.